Differential etching apparatus



June 20, 1967 D. M. sNoDDERLY, JR., ETAL. 3,326,792

DIFFERENTIAL ETCHING APPARATUS Filed Sept. 25. 1963 Ffa, 2 MM United States Patent O 3,326,792 DIFFERENTIAL ETCHING APPARATUS Donald Max Snodderly, Jr., Graduate Students Residence,

Rockefeller Institute, New York, N.Y. 10021, and Raymond Ehrenheck, 1 Cedar Bridge Drive, Bedford, Mass. 01730 Filed Sept. 25, 1963, Ser. No. 311,598

' 2 Claims. (Cl. 204-222) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to us of any royalty thereon. Y

This invention relates generally to etching apparatus and more particularly to a machine which is automatic in operation and which makes the etching process for microelectrodes repetitive. In addition, more precise control of the parameters involved in etching may be achieved.

The manufacture of microelectrodes requires a iinal geometry which is long, even and conically tapered, such that it terminates in a point with a diameter of the order of one micron. This shape is achieved by raising and lowering a wire into and out of a conducting solution while passing a low-voltage alternating current through the wire and the solution.

Prior art devices lhave utilized hydraulic means which are manually operated to dip an electrode into and out of the conducting solution. The manual operation of this type of device inhibits the precise repetition of the procedure; therefore, the end products do not have the reliability achieved by the instant invention.

Man-ual dipping arrangements fail to produce a desired velocity function which is repetitive. Accordingly, it is a primary object of this invention to provide an etching apparatus which is repetitive and provides precise control of the parameters of the end product.

It is another object of the invention to provide an apparatus which is significantly faster than present day microelectrode etchers while at the same time maintaining a control over quality not heretofore achieved.

It is a further object of this invention to provide an etching apparatus which is easily manufactured of conventional, currently available materials which lend themselves to mass production, manufacturing techniques.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, wherein:

FIGURE 1 is a perspective view of the etching apparatus of this invention with part of the electrical control systern schematically depicted; and

FIGURE 2 is a plot of the travel of the plunger in relation to the rotative angle of the cam to illustrate the displacement function.

Referring to FIGURE l, there is shown a shunt-wound D.C. motor which is connected to a suitable source of power (not shown). The motor 10 has a gear reducer 12 which drops the speed of the motor 10 and presents the drive at right angles to the axis of the motor with a suflicient torque for the operation of the remainder of the device. A iiexible coupling 14 is secured to the gear reducer and is also utilized to drive a cam 16 mounted on a shaft 18 which is suitably supported upon bearings 20. The cam 16 is utilized to control the dipping action of the electrodes into an etching solution; therefore, the cam is designed to produce the proper throw of a plunger 22 and the shape of the cam controls the velocity function governing the motion of the wire entering and leaving the fluid. Various velocity functions may be obtained merely by interchanging separate cams.

As can be seen in FIGURE 2, one desi-gn of the cam 16 in its rotation produces a linear displacement with respect to time with a slight rounding at the break points. This velocity function yields a gradual taper suitable for microelectrode work. Small variations in taper may be eected by changing the current through the wire during the etching process. The magnitude of the velocity may be regulated by choosing the proper armature current for the D.C. motor 10.

The plunger or throw-rod 22 is suitably mounted in bearing blocks 24 for guiding t-he plunger in a vertical direction and has a yoke 26 mounted on the end of the plunger 22 adjacent cam 16. A roller 28 mounted within the yoke bears against the cam 16 in order to receive motion from the cam and transmit it to the plunger. In order to bias the plunger 22 against the cam a spring 30 is inserted around the plunger and biases the plunger in an upward direction by bearing at its lower end on the lower bearing 24 and at its upper end by means of an adjustable collar 32 ailixed to the plunger rod.

The securing of electrodes 34 to the plunger is achieved by means of an electrode holder 36 which is releasably secured to the throw-rod 22. Releasable operation of the holder is achieved by means of spring biased balls 38 within the body of the holder which engage a groove 40 in the rod 22. A series of set screws 42 are provided around the outer periphery of the holder 36 in order to engage electrodes 34 inserted in holes within the holder in order to allow for engagement of the electrodes by the set screws.

Timing of the device is effected by means of a pair of gears 46, one of which is secured to cam shaft 18 and the other of which operates a counter 48 to indicate the number of revolutions of the cam and hence the number of dips executed by the electrode wires 34. If desired, a switch 50, schematically depicted, may be provided to cut the machine off automatically thereby rendering the counter and switch as an automatic timer. Alternatively, a unied timer unit may be utilized.

In order to utilize the machine for etching electrodes, wires 34 are inserted into the electrode holder 36 and secured by means of the set screws 42. The electrode holder is then pressed on the plunger in preparation for the immersion of the electrode into an etching solution. In order to facilitate the electrical attachment of the electrodes to a low voltage power source indicated at 52 a plug and socket 54 is utilized to disconnect a wire extending between these two elements. A container of etching solution with an inert carbon electrode is indicated schematically at 56.

Application of power to the motor 10 by means of a conventional switch 58 causes revolution of the flexible coupling 14 and the shaft 18 with cam 16 thereon. This rotation motion is transformed into a reciprocating motion by means of the spring biased plunger or throwrod 22 to effect alternate immersion and withdrawal of electrode wires 34 from ythe etching solution, the llow voltage power supply having been turned on simultaneously with t-he operation of the switch 58 in a conventional manner.

Since a large number of electrodes may be accurately controlled in their velocity function with this operation, the apparatus is capable of repetitive operation with accurate quality control. After the required number of dips have been effected, the counter indicates the manual shut down of the apparatus or alternatively the automatic switching arrangement 50 or a timer may shut the machine off.

Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

We claim 1. An apparatus for etching microelectrodes comprising: a holder for releasably securing a multiplicity of Wires to be made into microelectrodes, a throw-rod, means on lsaid throw-rod and said holder for releasably securing said holder to one end of said throw-rod, means acting on said throw-rod for biasing said throw-rod in a direction toward its other end, cam means shaped to provide a linear displacement with respect to time of said throwrod to control the velocity function to produce a tapered electrode, said cam being operatively connected with said other end of said throw-rod, means for rotating said cam to cause reciprocation of said throw-rod and said holder, a container of etchant solution beneath said holder, an electrode in said etchant solution, a power supply connecting said electrode and said wires, and means References Cited UNITED STATES PATENTS 1,376,379 4/1921 North 204-225 2,865,125 12/1958 Langfeld 41-9 3,130,141 4/1964 McMahon 204-224 3,235,475 2/1966 Williams 204-143 JOHN H. MACK, Primary Examiner.

W. VAN SISE, Examiner. 

1. AN APPARATUS FOR ETCHING MICROELECTRODES COMPRISING: A HOLDER FOR RELEASABLY SECURING A MULTIPLICITY OF WIRES TO BE MADE INTO MICROELECTRODES, A THROW-ROD, MEANS ON SAID THROW-ROD AND SAID HOLDER FOR RELEASABLY SECURING SAID HOLDER TO ONE END OF SAID THROW-ROD, MEANS ACTING ON SAID THROW-ROD FOR BIASING SAID THROW-ROD IN A DIRECTION TOWARD ITS OTHER END, CAM MEANS SHAPED TO PROVIDE A LINEAR DISPLACEMENT WITH RESPECT TO TIME OF SAID THROWROD TO CONTROL THE VELOCITY FUNCTION TO PRODUCE A TAPERED ELECTRODE, SAID CAM BEING OPERATIVELY CONNECTED WITH SAID OTHER END OF SAID THROW-ROD, MEANS FOR ROTATING SAID CAM TO CAUSE RECIPROCATION OF SAID THROW-ROD AND SAID HOLDER, A CONTAINER OF ETCHANT SOLUTION BENEATH SAID HOLDER, AND ELECTRODE IN SAID ETCHANT SOLUTION, A POWER SUPPLY CONNECTING SAID ELECTRODE AND SAID WIRES, AND MEANS FOR CONTROLLING THE NUMBER OF RECIPROCATIONS OF SAID THROW-ROD. 